BP imageOn Aug. 3, the new 75-ton cap sits atop the site of BP's Deepwater Horizon oil spill in the Gulf of Mexico.

BP engineers and a team of government scientists led by Energy Secretary Steven Chu were still studying the Macondo well Wednesday and planning to test pressure at the top of the well to determine the best way forward, National Incident Commander Thad Allen said.

Meanwhile, the blowout preventer that was being used for a second, backup, relief well is being removed for use on the Macondo well, Allen said.

Officials are concerned that pressure inside the well will rise when it is pumped with mud and cement during the procedure called a "bottom kill." The rise in pressure could damage the well's annulus, an outer shell, and possibly cause the release of about 1,000 barrels of oil believed to be trapped inside the annulus.

"We continue to assess the condition of the well," Allen said. He would not say when a final decision would be made.

A decision on how to relieve pressure inside the well during the bottom kill must be reached before Allen will give the go-ahead for BP to resume drilling on the relief well and tap into the
Macondo well.

The Discoverer Enterprise drill ship and the Q4000 platform were being positioned near the well Wednesday to purge the well so that further tests could be done, Allen said.

Based on the results, officials are expected to decide on one of two options for relieving pressure during the final kill procedure.

One is to remove the blowout preventer and capping stack on the well and put a new blowout preventer in its place. The second involves leaving the current equipment in place and building a pressure relief mechanism for the capping stack.

Technicians started moving the blowout preventer attached to the second, backup relief well to Macondo site Wednesday, Allen said. The apparatus will be used on the new well regardless of the team's conclusion, Allen said. It could be used to replace the capping stack and the original blow out preventer during the bottom kill.

But if the team decides not to replace the blowout preventer before the bottom kill, the blowout preventer will still be put on as part of the final step in the process of permanently abandoning the well.

Coast Guard photoShips and drilling rigs surround the Discoverer Enterprise as it works to recover oil from the Deepwater Horizon drill site on June 15.

Allen said Monday that a decision on how to relieve pressure would be made "in the next day or two," but on Wednesday said he had no timeline. Instead, Allen said, the sequence of events will be "conditions based."

"There wasn't a plan in place because this has never been done before," Allen said.

The relief well, designed to perform a bottom kill of the blown-out well by pumping it with mud and cement, has long been considered the ultimate solution for plugging the once-gushing well. But earlier this month, officials studying the Macondo well in preparation for the intercept grew concerned that the procedure might dislodge about 1,000 barrels of oil trapped inside the well, Allen said.

The oil is caught above a cement plug holding back oil from the subterranean reservoir and below a seal at the top of the well's annulus. The cement settled in the blowout preventer during the "static kill" procedure that successfully pushed all of the oil inside the well casing back into the reservoir.

The team is worried that pumping mud and cement into the space would increase pressure, causing the now-stagnant oil to displace the top seal and shoot up the well column, where it could damage the well's original blowout preventer and, perhaps, escape into the water.

Of particular concern is a piece of equipment that connects the original blowout preventer to a smaller blowout preventer atop it.

The apparatus, called a transition spool, can withstand pressure of up to 7,500 pounds per square inch.